1. Field of the Invention
The present invention relates to an endoscope having a small diameter, which is inserted in a blood vessel of a living body to observe its interior.
2. Description of the Related Art
An insertion portion of an endoscope which is inserted in a stomach, intestinum duodenum, or large intestine to observe its interior is constituted by a flexible tube portion, a bending tube portion, and a distal-end constituting portion. Upon operation of a bending operation knob provided at an operation portion, a pulling wire inserted through the insertion portion in the vertical and lateral directions is moved forward/backward, thereby bending the bending tube portion in a desired direction. Thus, the distal-end constituting portion can be inserted in a desired direction into a body cavity. Therefore, in the flexible tube portion, an outer tube made of a synthetic resin covers the outer surface of a metal flexible tube through a blade. In the bending tube portion, an outer tube made of a synthetic resin covers the outer surfaces of metal bending bridges through a blade. Image guide fibers, light guide fibers, an insertion channel, and the like are arranged inside the insertion portion.
The insertion portion of the endoscope incorporates the metal flexible tube and blade, i.e., members which do not transmit X-rays. Therefore, when the insertion portion is inserted in a body cavity and the interior of the body cavity is observed, if an X-ray imaging operation is performed by an external X-ray apparatus, the distal end position of the insertion portion can be confirmed.
However, the diameter of an insertion portion of an endoscope which is inserted in a very narrow internal cavity such as a blood vessel must be decreased as much as possible.
The insertion portion of the endoscope which is inserted in a very narrow internal cavity such as a blood vessel is constituted as disclosed in Published Unexamined Japanese Utility Model Application No. 61-203717 or as shown in FIGS. 5 to 7. More specifically, an endoscope main body 1 is constituted by an operation portion 2 and an insertion portion 3 to be inserted in a very narrow internal cavity such as a blood vessel. The outer surface of the insertion portion 3 is covered with an outer tube 4 made of a synthetic resin material. The outer tube 4 incorporates image guide fibers 5 and light guide fibers 6. An objective lens 7 is coupled to the distal end faces of the image guide fibers 5 through a metal lens frame 8.
In the endoscope with the above structure, the image guide fibers 5 and the objective lens 7 are coupled to each other through the metal lens frame 8 which does not transmit X-rays. When the insertion portion 3 is inserted in a body cavity and its interior is observed, if an X-ray imaging operation is performed by an external X-ray apparatus, the distal end position of the insertion portion 3 can be easily confirmed. However, when the lens frame 8 is used, a decrease in diameter of the insertion portion 3 is limited.
In order to eliminate this drawback, Published Unexamined Japanese Utility Model Application No. 61-143121 discloses a structure in which the lens frame 8 is omitted, and the diameter of the endoscope is further decreased. However, the image guide fibers 5, the light guide fibers 6, and the objective lens 7 of such a small-diameter endoscope are formed of glass which transmits X-rays. Since the lens frame 8 is omitted, there are no metal constituting elements, i.e., no members which do not transmit X-rays in the insertion portion 3. Therefore, even if the distal end position of the insertion portion 3 is to be confirmed by external X-ray imaging operation, it is impossible to do so.
An endoscope in which the image guide fibers 5 are covered with a coating layer 9, as shown in FIG. 5, is known as per Published Unexamined Japanese Patent Application No. 61-20009. Since the coating layer 9 is formed of a silicone resin which transmits X-rays, the position of the distal end portion of the insertion portion 3 cannot be confirmed.
U.S. Pat. No. 3,608,555 discloses a catheter in which an X-ray non-transmitting material is mixed in a synthetic resin tube. However, most of the X-ray non-transmitting materials include heavy metals. Therefore, if such a material containing a heavy metal is mixed in a portion which is brought into direct contact with a body fluid, this poses problems of affinity and noxiousness to a living body. Therefore, the synthetic resin tube cannot be employed as the outer tube of the insertion portion of the endoscope.
U.S. Pat. No. 4,027,659 discloses a medical tube in which an X-ray non-transmitting material is partially mixed along the longitudinal direction. This tube also poses the problems of affinity and noxiousness to a living body like in U.S. Pat. No. 3,608,555.
As described above, when the lens frame or the like is omitted to decrease the diameter of the insertion portion of the endoscope to be inserted in a blood vessel or the like, there are no X-ray non-transmitting materials in the insertion portion, and the position of the insertion portion cannot be confirmed by the external X-ray imaging operation. If a heavy metal material is mixed in the outer tube, the adverse influence on a living body is expected.